Pick tool and method for making same

ABSTRACT

A pick tool comprising an insert and a steel holder for the insert, the insert comprising a superhard tip joined to a cemented carbide support body having an insertion shank; the steel holder comprising a shaft for connection to a tool carrier and provided with a bore configured for receiving the insertion shank; the volume of the cemented carbide support body being at least 6 cm 3 .

This application claims the benefit of U.S. Provisional Application No.61/296,833 filed Jan. 20, 2010, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND

Embodiments of the invention relate generally to pick tools comprising asuperhard tip, particularly but not exclusively degrading hard orabrasive bodies, such as rock, asphalt, coal or concrete, for example,and to a method for making same.

Pick tools may be used for breaking, boring into or otherwise degradingstructures or bodies, such as rock, asphalt, coal or concrete and may beused in applications such as mining, construction and roadreconditioning. For example, in road reconditioning operations, aplurality of pick tools may be mounted on a rotatable drum and caused tobreak up road asphalt as the drum is rotated. A similar approach may beused to break up rock formations such as in coal mining. Some pick toolsmay comprise a working tip comprising synthetic diamond material, whichis likely to have better abrasion resistance than working tips formed ofcemented tungsten carbide material. However, synthetic and naturaldiamond material tends to be more brittle and less resistant to fracturethan cemented carbide material and this tends to reduce its potentialusefulness in pick operations. There is a need to provide a pick toolhaving longer working life.

United States patent application publication number 2008/0035383discloses a high impact resistant tool having a superhard materialbonded to a cemented metal carbide substrate, the cemented metal carbidesubstrate being bonded to a front end of a cemented metal carbidesegment, which has a stem formed in the base end, the stem being pressfit into a bore of a steel holder. The steel holder is rotationallyfixed to a drum adapted to rotate about an axis.

SUMMARY

Viewed from a first aspect, there can be provided a pick tool (alsoreferred to as a superhard pick tool) comprising an insert (alsoreferred to as a pick insert) mounted in a steel holder, the insertcomprising a superhard tip joined to a cemented carbide support body atan end of the support body, the support body comprising an insertionshank (also referred to simply as a shank); the steel holder having abore configured to accommodate the insertion shank and comprising ashaft configured for mounting the steel holder onto a tool carrier; suchas a pick driver apparatus; the volume of the cemented carbide supportbody being at least 6 cm³, at least 10 cm³ or at least 15 cm³. Theinsertion shank may be shrink-fitted within the bore. Viewed fromanother aspect there can be provided a kit of components for the presentpick tool, the kit being in an unassembled or partly assembled state.

Viewed from a second aspect, there can be provided a method for making apick tool, the method including providing an insert and a steel holderfor the insert, the insert comprising a superhard tip joined to acemented carbide support body having an insertion shank; the steelholder comprising a shaft for connection to a tool carrier, and providedwith a bore for receiving the insertion shank; the insertion shankhaving a volume of at least 15 cm³; and shrink fitting the insertionshank into the bore of the steel holder.

Viewed from a third aspect, there can be provided a method ofdisassembling a pick tool, the method including heating the steel holderto expand the bore and withdrawing the insertion shank from the bore.

BRIEF INTRODUCTION TO THE DRAWINGS

Non-limiting example arrangements to illustrate the present disclosureare described hereafter with reference to the accompanying drawings, ofwhich:

FIG. 1A shows a schematic partially cut-away side view of an example ofa pick tool.

FIG. 1B shows a schematic side view of the pick insert of the examplepick tool shown in FIG. 1A.

FIG. 1C shows a partially cut-away perspective view of the steel holderof the example pick tool shown in FIG. 1A.

FIG. 2 shows a schematic partially cut-away side view of an example of apick tool.

FIG. 3 shows a schematic partially cut-away side view of an example of apick tool.

FIG. 4 shows a schematic partially cut-away side view of an example of apick tool, in which dimensions are in millimetres.

FIG. 5 shows a schematic partially cut-away side view of an example of apick tool, in which dimensions are in millimetres.

FIG. 6 shows a schematic partially cut-away side view of an example of apick tool, in which dimensions are in millimetres.

FIG. 7 shows a schematic longitudinal cross section view of the exampleof a superhard tip and part of the support body of any one of theexample pick tools shown in FIG. 1A to FIG. 6.

FIG. 8 shows a schematic side view of an example of a superhard tip andpart of the support body of any one of the example pick tools shown inFIG. 1A to FIG. 6, in which dimensions are in millimetres and angles arein degrees.

FIG. 9 shows a schematic partially cut-away side view of an example of apick tool mounted to a carrier body, in which only a portion of the picktool is shown.

FIG. 10 shows a schematic side view an example of a pick tool for adifferent carrier than that illustrated in FIG. 9.

FIG. 11 shows a schematic partially cut-away side view of an example ofa pick tool, with a section of the steel holder in a worn-awaycondition.

The same reference numbers refer to the same general features in alldrawings.

DETAILED DESCRIPTION

As used herein, “superhard” means a Vickers hardness of at least 25 GPa,and a superhard tool, insert or component means a tool, insert orcomponent comprising a superhard material.

Synthetic and natural diamond, polycrystalline diamond (PCD), cubicboron nitride (cBN) and polycrystalline cBN (PCBN) material are examplesof superhard materials. As used herein, synthetic diamond, which is alsocalled man-made diamond, is diamond material that has been manufactured.As used herein, polycrystalline diamond (PCD) material comprises a mass(an aggregation of a plurality) of diamond grains, a substantial portionof which are directly inter-bonded with each other and in which thecontent of diamond is at least about 80 volume percent of the material.Interstices between the diamond grains may be at least partly filledwith a binder material comprising a catalyst material for syntheticdiamond, or they may be substantially empty. As used herein, a catalystmaterial for synthetic diamond is capable of promoting the growth ofsynthetic diamond grains and or the direct inter-growth of synthetic ornatural diamond grains at a temperature and pressure at which syntheticor natural diamond is thermodynamically stable. Examples of catalystmaterials for diamond are Fe, Ni, Co and Mn, and certain alloysincluding these. Bodies comprising PCD material may comprise at least aregion from which catalyst material has been removed from theinterstices, leaving interstitial voids between the diamond grains. Asused herein, PCBN material comprises grains of cubic boron nitride (cBN)dispersed within a matrix comprising metal or ceramic material.

Other examples of superhard materials include certain compositematerials comprising diamond or cBN grains held together by a matrixcomprising ceramic material, such as silicon carbide (SiC), or cementedcarbide material, such as Co-bonded WC material (for example, asdescribed in U.S. Pat. Nos. 5,453,105 or 6,919,040). For example,certain SiC-bonded diamond materials may comprise at least about 30volume percent diamond grains dispersed in a SiC matrix (which maycontain a minor amount of Si in a form other than SiC). Examples ofSiC-bonded diamond materials are described in U.S. Pat. Nos. 7,008,672;6,709,747; 6,179,886; 6,447,852; and International Applicationpublication number WO2009/013713).

Example arrangements of pick tools for degrading hard or abrasive bodiesor structures are described with reference to FIG. 1A to FIG. 6.

Examples of pick tools 100 comprise an insert 110 and a steel holder 120for the insert 110. The insert 110 comprises a superhard tip 112 joinedto a cemented carbide support body 114 comprising an insertion shank118. In these examples, the insertion shanks 118 are generallycylindrical in shape and have a mean diameter D, the superhard tips 112comprise respective PCD structures 111 bonded to cemented carbidesubstrates 113, which are joined to respective support bodies 114 atrespective interfaces 115 by means of braze material, and the supportbodies 114 have generally frusto-conical portions 116 to which thesuperhard tips 112 are brazed. The steel holders 120 comprise shafts 122for connection to a pick drum device (not shown), and a bore 126 areconfigured for shrink-fitting the insertion shanks 118. The steelholders 120 may be provided with respective insert receiver members 124in which the bores 126 are formed.

At least a portion of the insertion shank 118 may be secured within thebore 126 by means of a shrink fit. As used herein, a shrink fit is akind of interference fit between components achieved by a relative sizechange in at least one of the components (the shape may also changesomewhat). This is usually achieved by heating or cooling one componentbefore assembly and allowing it to return to the ambient temperatureafter assembly. Shrink-fitting is understood to be contrasted withpress-fitting, in which a component is forced into a bore or recesswithin another component, which may involve generating substantialfrictional stress between the components.

Shrink-fitting is likely to result in a region (not indicated) of thesteel holder 120 adjacent the bore 126 being in a static state ofcircumferential tensile stress. In some examples of pick tools, a regionwithin the steel holder adjacent the bore may be in a state ofcircumferential (or hoop) static tensile stress of at least about 300MPa or at least about 350 MPa, and in some pick tools, thecircumferential static tensile stress may be at most about 450 MPa or atmost about 500 MPa. As used herein, the static stress state of a tool orelement refers to the stress state of the tool or element under staticconditions, such as may exist when the tool or element is not in use.

In some example pick tools, a portion 119 of the support body 114,including the frusto-conical portion 116, may protrude from the steelholder 120 and extend beyond a mouth 128 of the bore 126. In someexamples, the diameter of the protruding portion 119 along the entirelength of the protruding portion may be at most about 5% greater, orsubstantially no greater than the mean diameter D of the bore 126. Inthe examples illustrated in FIG. 1A to FIG. 6, the diameter of theprotruding portion 119 does not substantially exceed that of the bore126.

In one embodiment, a collar encloses at least part of a protrudingportion of the cemented carbide support body, and in one embodiment thecollar may be shrink-fitted onto the protruding portion. In oneembodiment, the collar has lower hardness and abrasive wear resistancethan cemented carbide, and in one embodiment the collar comprises steel.In one example, the collar is joined to the steel holder by means ofbrazing. The collar may provide support or protection for the cementedcarbide support body.

With reference to the example pick tool variants shown in FIG. 2 andFIG. 4, a collar 130 encloses part of the protruding portion 119 of thesupport body 114. The collar 130 may enclose at least part of theprotruding portion 119, and in one example the collar 130 may beshrink-fitted onto the protruding portion. The collar 130 may have lowerhardness and abrasive wear resistance than cemented carbide and maycomprise steel. In one embodiment, the collar 130 is joined to the steelholder 120 by means of brazing. The collar 130 may provide support orprotection for the cemented carbide support body 114. The collar 130 mayhave various shapes, such as generally conical or generally rounded, andit may be substantially symmetrical or non-symmetrical. At least part ofthe outer surface of the collar 130 may be protected by means of a wearprotective hard facing (not shown), for example a layer or sleevecomprising tungsten carbide. In particular, at least a part 127 of theouter surface of the steel holder 120 adjacent the mouth 128 of the bore126, for example a surface region of the insert receiver member 124extending up to 20 mm from the mouth 127, may be protected by means of awear protective means (not shown). Examples of such means may be a layeror sleeve comprising tungsten carbide and/or grains of superhardmaterial such as diamond or cBN. In one example embodiment, the collar130 may have a protective hard facing disposed mainly or only on a sidethat would be exposed to greater wear in use.

With reference to FIG. 3, a major portion of the insertion shank 118 issecured within the bore 126 of the steel holder 120 by means of a shrinkfit. In this example, the insert receiver member 124 is provided with aseat 129 against which the insertion shank 118 of the support body 114may be positioned. The seat 129 may be provided with a through-hole 1291for facilitating extraction of the insert 112 or brazing the end of theinsertion shank 118 to the seat 129. For example, the through-hole 1291of the seat 129 may have a diameter S of at least about 0.6 cm and atmost about 2 cm. The insert receiver member 124 may have an outerdimension W, which may be about 4.8 cm. In general, the greater thediameter D of the insertion shank 118 of the support body 114, thethinner the wall of the insert receiver member 124 defining the bore 126may need to be, since the external dimensions of the steel holder 120may be constrained by the design of the pick apparatus (not shown) orthe requirements of the pick operation. For example, the thicker thewall of the insert receiver member, the more robust the pick tool islikely to be in general, but as a trade-off, the energy requirement ofthe operation and wear of the steel are likely to be higher.

In the examples illustrated in FIG. 1A, FIG. 2 and FIG. 4, the bore 126may extend through the holder 120, providing a through-hole having apair of opposite open ends (or mouths) 128. In these examples, least aportion of the insertion shank 118 may extend substantially through theinsert receiver member 124.

In some examples of pick tools, the ratio of the volume of the cementedcarbide support body to the volume of the superhard structure is atleast about 30, at least about 40 or at least about 50. In someembodiments, the ratio of the volume of the cemented carbide supportbody to the volume of the superhard structure is at most about 300, atmost about 200 or at most about 150. In some embodiments, the volume ofthe superhard structure is at least about 200 mm³ or at least about 300mm³. In some embodiments, the volume of the superhard structure is atmost about 500 mm³ or at most about 400 mm³.

In some variants of pick holders, the length of the bore may be at leastequal to its diameter. In one example, the diameter of the insertionshank and the bore may be about 2.5 cm and the length of the bore andthe inserted portion of the insertion shank may be about 6 cm; andtherefore the volume of the bore and the inserted portion of theinsertion shank may be about 29 cm³ and the area of contact between theinternal peripheral surface of the bore and the insertion shank may beabout 47 cm². In another example, the diameter of the insertion shankand the bore may be about 2 cm and the length of the bore and theinserted portion of the insertion shank may be about 8.3 cm; andtherefore the volume of the bore and the inserted portion of theinsertion shank may be about 26 cm³ and the area of contact between theinternal peripheral surface of the bore and the insertion shank mayabout 52 cm². In yet another example, the diameter of the insertionshank and the bore may be about 3.5 cm and the length of the bore andthe inserted portion of the insertion shank may be about 6.9 cm;therefore the volume of the bore and the inserted portion of theinsertion shank may be about 66 cm³ and the area of contact between theinternal peripheral surface of the bore and the insertion shank may beabout 76 cm².

In some examples of pick tools, the insertion shank may not besubstantially cylindrical and may exhibit any of various shapes whenviewed in transverse cross section. For example, insertion shank may begenerally elliptical, egg-shaped, wedge-shaped, square, rectangular,polygonal or semi-circular in shape; or the cross-sectional shape of theinsertion shank may vary along its length.

In some examples, the shank may have a substantially cylindrical formand may have a diameter of at least about 15 mm, at least about 20 mm,at least about 25 mm or even at least 30 mm. In some embodiments, theshank has a diameter of at most about 20 mm, at most about 25 mm, atmost about 30 mm, at most about 35 mm, or even at most about 40 mm. Insome embodiments, the diameter of the shank varies by less than about 5mm along its entire length, or the diameter is substantially invariantalong its entire length.

The table below summarises certain example combinations of approximatedimensions that may be used with variants of pick tools disclosedherein. The dimensions relate to the length of the bore and the lengthof the inserted portion of the insertion shank, the mean diameter of thebore and of the inserted portion of the insertion shank, the minimumvolume of the bore and the volume of the inserted portion of theinsertion shank; and the area of contact between the peripheral internalwall of the bore and the corresponding surface of the inserted portionof the insertion shank.

a b c d e f g Bore length/depth 7.0 7.7 4.9 6.5 6 6.5 6.7 L of insertionof shaft, cm Bore/insertion 2.0 2.0 2.5 2.5 2.5 3.0 3.5 shank diameterD, cm Volume of bore/ 22 24 24 32 29 46 64 inserted portion of shaft,cm³ Area of contact of 44 48 38 51 47 61 73 bore and insertion shank,cm²

In some embodiments, the support body comprises a cemented carbidematerial having fracture toughness of at most about 17 MPa·m^(1/2), atmost about 13 MPa·m^(1/2), at most about 11 MPa·m^(1/2) or even at mostabout 10 MPa·m^(1/2). In some embodiments, the support body comprises acemented carbide material having fracture toughness of at least about 8MPa·m^(1/2) or at least about 9 MPa·m^(1/2). In some embodiments, thesupport body comprises a cemented carbide material having transverserupture strength of at least about 2,100 MPa, at least about 2,300 MPa,at least about 2,700 MPa or even at least about 3,000 MPa.

In some embodiments, the support body comprises a cemented carbidematerial comprising grains of metal carbide having a mean size of atmost about 8 microns or at most about 3 microns. In one embodiment, thesupport body comprises a cemented carbide material comprising grains ofmetal carbide having a mean size of at least about 0.1 microns.

In some embodiments, the support body comprises a cemented carbidematerial comprising at most about 13 weight percent, at most about 10weight percent, at most about 7 weight percent, at most about 6 weightpercent or even at most about 3 weight percent of metal binder material,such as cobalt (Co). In some embodiments, the support body comprises acemented carbide material comprising at least about 1 weight percent, atleast about 3 weight percent or at least about 6 weight percent of metalbinder.

In some examples, the support body may consist essentially of, orconsist of cemented carbide material.

In some examples of pick tools, the shrink-fitting of the components maybe reversible and the steel holder and/or the insertion shank may bedetached and reused, which may in effect reduce the cost of the picktool and permit extended use of the steel holder. This could be achievedby heating the steel holder in the vicinity of the bore to cause it toexpand relative to the cemented carbide insertion shank, permitting theinsertion shank to be removed from the bore.

A method for making a pick tool is provided, the method includingproviding a pick insert comprising a superhard tip joined to a cementedcarbide support body at an end of the support body, the support bodycomprising a shank (insertion shank); providing a steel holder having abore configured to accommodate the shank and comprising a shaft suitablefor mounting the holder onto a tool carrier; and shrink-fitting theshank into the bore of the steel holder. The insertion shank may beshrink-fitted into the bore of the steel holder by heating at least thepart of the steel holder including the bore to a temperature of about350 degrees centigrade, inserting the shank into the bore of the heatedholder and allowing the bore of the steel holder to cool and shrink,thereby holding the insertion shank in compression. In examples wherethe steel holder comprises a seat, the insertion shank may be insertedall the way into the bore so that the inserted end abuts the seat.

The interference between the insertion shank and the bore of the holderis the difference in size between them, which may be expressed as apercentage of the size. For example, in embodiments where the insertionshank (and the bore) has a generally circular cross section, theinterference may be expressed as the difference in diameter as apercentage of the diameter. The dimension between the insertion shankand the bore would be expected to be selected depending at least on thediameter of the insertion shank, and may be at least about 0.002 percentof the diameter of the insertion shank. In one example, the diameter ofthe insertion shank is about 2.5 cm and the interference between theinsertion shank and the bore is about 0.08 percent of the diameter ofthe insertion shank. The interference between the insertion shank andthe bore may be at most about 0.3 percent of the diameter of thediameter of the insertion shank. If the interference is too great, theelastic limit of the steel material of the holder may be exceeded whenthe steel holder is shrink-fitted onto the onto the insertion shank,resulting in some plastic deformation of the steel adjacent the bore. Ifthe interference is not high enough, then the shrink fit may not besufficient for the insert to be held robustly by the holder in use.

In some versions of the method, the precise dimensions of the insertionshank and the bore may be selected such that after shrink-fitting theinsertion shank into the bore, a region within the steel holder adjacentthe bore is in a state of circumferential (or hoop) static tensilestress of at least about 300 MPa or at least about 350 MPa. In someembodiments, a region within the steel holder adjacent the bore is in astate of circumferential (or hoop) static tensile stress of at mostabout 450 MPa or at most about 500 MPa.

As a non-limiting example, a pick tool as disclosed may comprise asuperhard tip as described in United States patent applicationpublication numbers 2009/0051211; 2010/0065338; 2010/0065339 or2010/0071964. With reference to FIG. 7, an example of an insert for anembodiment of a pick tool as disclosed herein comprises a superhard tip112 comprising a superhard structure 111 in the general form of a capbonded to a cemented carbide substrate 113. The superhard tip 112 isjoined to a frusto-conical portion 116 of a support body 114. The majorpart of the superhard structure 111 has a spherically blunted conicalouter shape, having a rounded apex 1111 with a radius of curvature in alongitudinal plane, and a cone angle κ between an axis parallel to thelongitudinal axis AL and conical portion 1112 of the outer surface ofthe superhard structure 111. The superhard structure 111 comprises anose region 1113 and a skirt region 1114, which depends longitudinallyand laterally away from the nose region 1113. In some versions of theexample, the minimum longitudinal thickness of the skirt region 1114 maybe at least about 1.3 mm or at least about 1.5 mm. In some versions ofthe example, the longitudinal thickness of the superhard cap 111 at theapex 1111 is at least about 4 mm or at least about 5 mm and at mostabout 7 mm or at most about 6 mm. In one version of the example, thelongitudinal thickness of the superhard structure 111 at the apex 1111is in the range from about 5.5 mm to 6 mm. In some versions of theexample, the radius of curvature of the rounded apex 1111 is at leastabout 2 mm and at most about 3 mm. In some embodiments, the cone angle κis at most 80 degrees or at most 70 degrees. In some versions of theexample, the cone angle κ is at least 45 degrees or at least 50 degrees.

With reference to FIG. 8, an example of an insert for an embodiment of apick tool as disclosed comprises a superhard tip 112 comprising asuperhard structure 111 bonded to a cemented carbide substrate 113. Thesuperhard tip 112 is joined to a frusto-conical portion 116 of a supportbody 114. The radius of curvature R of the spherically blunted cone nose1111 is about 2.25 mm and the cone angle κ is about 42 degrees.

With reference to FIG. 9, a part of an example of a steel holder 120 fora pick tool as disclosed is attached to a base block 200 (carrier body)by means of an interlocking fastener mechanism 210 in which the shaft122 of the steel holder 120 is locked within a bore formed within thecarrier body 200. Part of the insertion shank 118 of an example picktool is also shown. The shaft 122 may be releasably connectable to thebase block 200 welded or otherwise joined to the drum. The base block200 and holder 120, more specifically the shaft 122, may be configuredto permit releasable inter-engagement of the steel holder 120 and baseblock. The shaft 122 may be configured to inter-engage non-rotationallywith a base block, and may be suitable for use with tool carriersdisclosed in German patents numbers DE 101 61 713 B4 and DE 2004 057 302A1, for example. The tool carrier, such as a base block, may be weldedonto a component of a drive apparatus, such as a drum, for driving thesuperhard pick tool. FIG. 10 shows a side view of a pick tool 100 for adifferent tool carrier than the example illustrated in FIG. 9, the shaft122 of the steel holder 120 being configured differently. The pick tool100 comprises an insert 110 with a superhard tip 112 joined to a portion116 of a support body.

A method is provided for attaching a superhard pick tool to a toolcarrier joined to a component for a drive apparatus, the methodincluding joining a pick insert to a steel holder to form a pick tool,the steel holder comprising a shaft configured operable to attach thesteel holder onto the tool carrier, the tool carrier comprising anengagement means configured to receive the shaft of the steel holder;and then attaching the superhard pick tool to the tool carrier. In oneembodiment of the method, the tool carrier is welded onto a component ofa drive apparatus, such as a drum, for driving the superhard pick tool.

In operation, the pick tool may be driven forward by a drive apparatuson which it is mounted, against a structure to be degraded and with thesuperhard tip at the leading end. For example, a plurality of pick toolsmay be mounted on a drum for asphalt degradation, as may be used tobreak up a road for resurfacing. The drum is connected to a vehicle andcaused to rotate. As the drum is brought into proximity of the roadsurface, the pick tools are repeatedly impacted into the road as thedrum rotates and the leading superhard tips thus break up the asphalt. Asimilar approach may be used to break up coal formations in coal mining.

With reference to FIG. 11, the example pick tool illustrated in FIG. 5is shown schematically in a worn condition, in which a part 1201 of thesteel holder 120 has been worn away in use to expose part of the surfaceof the insertion shaft 118 to which that part 1201 had been adjacent.

Although the example pick tool illustrated in FIG. 11 is shown in a worncondition, some example pick tools may be provided with a cut-awayportion 1201 prior to use. In this configuration, the insertion shank118 is only partially surrounded by the bore 126 at a range of axialpositions R along the length L of the insertion shank 118 (i.e. withinthe range R of axial positions, the insertion shank 118 is not entirelysurrounded or enclosed by the steel holder 120).

When designing pick tools for highly abrasive operations such asasphalt, coal or potash degradation, it would be desirable to achieve abalance between the cost of the tool and its resistance to abrasive wearand fracture in use. Superhard materials such as synthetic diamond tendto be much more abrasion resistant but also much more costly thancemented carbide materials, which in turn tend to be much more abrasionresistant but much more costly than steel materials. One approach may beto minimise the amounts of diamond-containing and cemented carbidematerials in the tool according to their relative costs and to configurecomponents comprising these materials so as to achieve an acceptabletool life.

A cemented carbide support body having a relatively large volume of atleast about 6 cm³, at least about 10 cm³ or at least about 15 cm³arranged behind the PCD tip in the direction of movement in use andextending relatively deeply into the steel holder seems to improve theworking life of the tool to a surprising degree that is likely tojustify additional cost of the carbide material.

While wishing not to be bound by a particular theory, the high densityand relatively high mass of the carbide insertion shank, as well as itshigh stiffness may provide substantially improved support for the PCDtip by tending to resist deformation or bending of the tip when it isthrust against the structure being broken. The carbide insertion shankmay be viewed as forming a spine-like structure extending relativelydeeply into the steel holder. The elongate carbide insertion shank mayalso function as a stiffening spine extending into the steel holder andmaking it more robust.

It has been found that a superhard-tipped pick tool having thecombination of a relatively large insertion shank and a shrink-fitconnection of the insertion shank within the steel holder exhibitsextended working life in an asphalt degradation operation. If the volumeof the inserted portion of the insertion shank is less than about 6 cm³or less than about 15 cm³, there may be insufficient support for thesuperhard tip in operation; and if the interface area between theinsertion shank and the bore is less than about 20 cm², the carbidesupport body may not be sufficiently robustly gripped by the steelholder into which it is shrink-fitted. If the diameter of the insertionshank is less than about 2 cm, it may not provide adequate support androbustness for the tool, which may break in particularly harshoperations, and/or the steel holder may wear excessively. If the lengthof the support body is less than about 4 cm, it may not providesufficient support for the steel holder and/or the PCD tip, which mayfracture prematurely.

In pick tools disclosed herein, in which the volume of the insertionshank and the bore as well as the area of contact between them arerelatively high, shrink-fitting the insertion shank into the steelholder may have benefits over press-fitting. Considerably less forcewould be required to shrink fit the relatively large insertion shankthan would be needed to press it into the bore. This may have the aspectthat the insert can be held securely enough within the bore of the steelholder without the elastic limit of the steel material beingsubstantially exceeded, thereby reducing plastic deformation of thesteel holder. While wishing not to be bound by a particular theory, thismay have the aspect that a region of the steel holder adjacent the boremay suffer less deformation and axial stress arising from the pressingforce and friction between the insertion shank and the bore surface. Theinsertion shank may also have reduced residual stress components, whichmay result in greater resistance to fracture in use. As a trade-off,shrink-fitting may require somewhat more sophisticated equipment andprocedure.

Shrink-fitting may permit reduced reliance on brazing to join the insertto the steel holder. This may be particularly useful where the superhardtip comprises synthetic or natural diamond, for example polycrystallinediamond, because of reduced thermal degradation of the tip as a resultof brazing, which requires the use of high temperature (diamond,particularly in PCD form, tends to have a relatively low thermalstability and to convert into graphite at high temperatures).Additionally, brazing may need to be carried out in a special furnaceand a special atmosphere, which may not be required for shrink fitting.

Example pick tools are provided. The following clauses are offered asfurther descriptions of the disclosed pick tools.

-   1. A superhard pick tool (for brevity, also referred to as a pick    tool) comprising an insert and a steel holder for the insert, the    insert comprising a superhard tip joined to a cemented carbide    support body having an insertion shank; the steel holder comprising    a shaft for connection to a tool carrier and the steel holder    provided with a bore configured for receiving the insertion shank;    the volume of the cemented carbide support body being at least 6    cm³, at least 10 cm³ or at least 15 cm³.-   2. A pick tool comprising an insert and a steel holder for the    insert, the insert comprising a superhard tip joined to a cemented    carbide support body having an insertion shank; the steel holder    comprising a shaft for connection to a tool carrier and the steel    holder provided with a bore configured for receiving the insertion    shank; an inserted portion of the insertion shank being secured in    the bore; the inserted portion having an axial length and a mean    diameter; the axial length being no less than the mean diameter.-   3. The pick tool of clause 2, in which the axial length of the    inserted portion is at least about 4 cm and at most about 8.5 cm.-   4. The pick tool of clause 2 or clause 3, in which the mean diameter    of the inserted portion is at least about 2 cm and at most about 3.5    cm.-   5. A pick tool comprising an insert and a steel holder for the    insert, the insert comprising a superhard tip joined to a cemented    carbide support body having an insertion shank; the steel holder    comprising a shaft for connection to a tool carrier and the steel    holder comprising an insert receiver member provided with a bore    configured for receiving the insertion shank; an inserted portion of    the insertion shank being secured in the bore and abutting a surface    area of the bore; the magnitude of the abutted surface area being    greater than the magnitude of the volume of the inserted portion.-   6. The pick tool of clause 5, in which the magnitude of the abutted    surface area is at least about 20 cm² and the volume of the inserted    portion is at least about 15 cm³.-   7. The pick tool of any one of the preceding clauses, in which the    insertion shank is shrink-fitted within the bore.-   8. A superhard pick tool (for brevity, also referred to herein    simply as “pick tool”) comprising a pick insert mounted to a steel    holder, the pick insert (for brevity, also referred to herein simply    as “insert”) comprising a superhard tip joined to a cemented carbide    support body at an end of the support body, the support body    comprising a shank (also referred to herein as “insertion shank”);    the steel holder having a bore configured to accommodate the    insertion shank and comprising a shaft configured for mounting the    holder onto a tool carrier; the shank being shrink fitted within the    bore of the steel holder.-   9. The pick tool of any one of the preceding clauses, in which the    insertion shank (shank) has a volume of at least 15 cm³.-   10. The pick tool of any one of the preceding clauses, in which a    surface area of the insertion shank abuts a corresponding inner    peripheral (side) surface area of the bore, the surface area being    at least 20 cm².-   11. The pick tool of any one of the preceding clauses, in which the    insertion shank has a diameter (or a mean diameter) of at least 1.5    cm or at least 2 cm and at most 4.0 cm or at most 3.5 cm.-   12. The pick tool of any one of the preceding clauses, in which the    lengths of the insertion shank and the bore are each at least about    4 cm.-   13. The pick tool of any one of the preceding clauses, in which the    ratio of the volume of the cemented carbide support body to the    volume of the superhard tip is at least 30 and at most 300, and the    volume of the superhard tip is at least 200 mm³ and at most 500 mm³.-   14. The pick tool of any one of the preceding clauses, in which the    volume of the superhard structure is least 0.2 cm³.-   15. The pick tool of any one of the preceding clauses, in which at    least a portion of the insertion shank is substantially cylindrical    in shape.-   16. The pick tool of any one of the preceding clauses, in which the    bore has a length that is at least equal to its diameter.-   17. The pick tool of any one of the preceding clauses, in which the    interference between the insertion shank and the bore is at least    about 0.002 percent of the diameter of the insertion shank and at    most about 0.3 percent of the diameter of the diameter of the    insertion shank.-   18. The pick tool of any one of the preceding clauses, in which a    region of the steel holder adjacent the bore is in a state of    circumferential (or hoop) static tensile stress of at least about    300 MPa and at most about 500 MPa.-   19. The pick tool of any one of the preceding clauses, in which the    diameter of the insertion shank varies by less than about 5 mm along    its entire length, or the diameter, and is substantially invariant    along its entire length.-   20. The pick tool of any one of the preceding clauses, in which a    portion of the insertion shank is only partly surrounded by the bore    of the steel holder (at a range of axial positions along the length    of the insertion shaft).-   21. The pick tool of any one of the preceding clauses, in which the    steel holder is provided with a seat for supporting an end of the    cemented carbide support body. The bore may communicate with the    outside of the steel holder through a passage or aperture provided    through or adjacent the seat.-   22. The pick tool of any one of the preceding clauses, in which the    bore extends through the holder, providing a through-hole having a    pair of open ends.-   23. The pick tool of any one of clauses 1 to 21, in which the bore    is substantially closed at one end.-   24. The pick tool of any one of the preceding clauses, in which a    portion of the cemented carbide support body protrudes from the    steel holder and extends beyond a mouth of the bore.-   25. The pick tool of clause 24, in which the diameter of the    protruding portion of the cemented carbide support body along the    entire length of the protruding portion is at most 5% greater than    the diameter of the mouth of the bore from which it protrudes.-   26. The pick tool of clause 24, comprising a collar enclosing or    surrounding at least part of the protruding portion.-   27. The pick tool of any one of the preceding clauses, in which the    insertion shank has a diameter of at least about 15 mm, at least    about 20 mm, at least about 25 mm or even at least 30 mm (in some    embodiments, the insertion shank may have a diameter of at most    about 20 mm, at most about 25 mm, at most about 30 mm, at most about    35 mm, or even at most about 40 mm).-   28. The pick tool of any one of the preceding clauses, in which the    superhard tip comprises natural or synthetic diamond material or cBN    material.-   29. The pick tool of any one of the preceding clauses, in which the    superhard tip comprises a polycrystalline diamond structure bonded    to a cemented carbide substrate.-   30. The pick tool of any one of the preceding clauses, in which the    superhard tip comprises diamond grains dispersed in a matrix    comprising SiC material, or diamond grains dispersed in a matrix    comprising cemented carbide material.-   31. The pick tool of any one of the preceding clauses, in which the    cemented carbide support body comprises cemented carbide material    having fracture toughness of at least 8 MPa·m^(1/2) and at most 17    MPa·m^(1/2).-   32. The pick tool of any one of the preceding clauses, in which the    cemented carbide support body comprises cemented carbide material    comprising at most 13 weight percent and at least 1 weight percent    metal binder material.-   33. The pick tool of any one of the preceding clauses in which the    support body comprises superhard material (for example, the support    body may comprise diamond or cBN grains dispersed within a cemented    carbide matrix).-   34. The pick tool of any one of the preceding clauses, for pavement    or road degradation, or for coal or potash mining.-   35. The pick tool of any one of the preceding clauses, in which the    tool carrier is welded or weldable onto a component of a drive    apparatus, such as a drum, for driving the superhard pick tool.-   36. The pick tool of any one of the preceding clauses, in which the    tool carrier comprises or is connectable to a drive or drivable    apparatus.-   37. A method for making a pick tool of any one of the preceding    clauses, the method including providing an insert and a steel holder    for the insert, the insert comprising a superhard tip joined to a    cemented carbide support body having an insertion shank; the steel    holder comprising a shaft for connection to a tool carrier and the    steel holder provided with a bore for receiving the insertion shank;    the insertion shank having a volume of at least 6 cm³, at least 10    cm³ or at least 15 cm³; and shrink fitting the insertion shank into    the bore of the steel holder.-   38. The method of clause 37, including selecting the interference    between the insertion shaft and the bore such that after    shrink-fitting the insertion shaft into the bore, a region within    the steel holder adjacent the bore is in a state of circumferential    static tensile stress of at least about 300 MPa and at most about    500 MPa, or substantially below the elastic limit of the steel    material comprised in the steel holder.

A non-limiting example of a pick tool is described in more detail below.

A superhard tip comprising PCD integrally attached to a cobalt-cementedtungsten carbide (Co—WC) substrate as illustrated in FIG. 8 was brazedto a support body. The PCD structure had a volume of about 382 mm³. Thesupport body was formed of Co—WC comprising about 13 weight percent Coand having a fracture toughness of about 16.3 MPa·m^(1/2) and transverserupture strength (TRS) of at least about 2,200 MPa. In another example,the support body was formed of Co—WC comprising about 8 weight percentCo and having a fracture toughness of about 14.6 MPa·m^(1/2) andtransverse rupture strength (TRS) of at about 2,800 MPa. The supportbody comprised a substantially cylindrical insertion shank and afrusto-conical end portion to which the PCD tip was brazed. Theinsertion shank had a surface finish in the range from about 0.04microns Ra to about 0.5 microns Ra. The diameter of the insertion shankwas 2.5 cm and its length was 6.7 cm.

A steel holder formed of 42Cr—Mo4 grade of steel and comprising aninsertion receiver member with a bore was provided, the diameter of thebore being about 2.5 cm and its length being about 6.7 cm. An annularseat was provided at the bottom end of the bore. The insertion shank wasshrink-fitted into the bore of the steel holder by heating the insertionreceiver member of the steel holder in air to a temperature of about 350degrees centigrade, inserting the shaft into the bore of the heatedholder and allowing the insertion receiver member to shrink onto theinsertion shank, thereby holding it in compression. The insertion shankwas inserted all the way into the bore so that the inserted end abuttedthe annular seat. The volume of the inserted portion of the insertionshank was therefore about 33 cm³ and the interface area between theinsertion shank and the peripheral internal wall of the bore was about53 cm². The interference between the insertion shank and the bore wasabout 0.02 mm and the static tensile hoop stress of the region of thesteel holder adjacent the bore was estimated to be in the range fromabout 300 MPa to about 500 MPa.

Pick tools according to the present example have been tested in roadreconditioning operations, in which they were mounted onto drums andused to degrade road asphalt. These were still in working conditionafter degrading at least about 20 km of road.

Various example embodiments of pick tools and methods for assembling andconnecting them have been described above. Those skilled in the art willunderstand that changes and modifications may be made to those exampleswithout departing from the spirit and scope of the claimed invention.

1-31. (canceled)
 32. A pick tool comprising an insert mounted in a steelholder, the insert comprising a superhard tip joined to a cementedcarbide support body at an end of the support body, the support bodycomprising an insertion shank; the steel holder having a bore configuredto accommodate the insertion shank and comprising a shaft configured formounting the steel holder onto a tool carrier; the cemented carbidesupport body having a volume of at least 15 cubic centimetres (cm³) andcomprising cemented carbide material having fracture toughness of atleast 8 megapascals times square root metre (MPa·m^(1/2)) and at most 17MPa·m^(1/2); in which an inserted portion of the insertion shank issecured in the bore, the inserted portion having an axial length of atleast 4 centimetres (cm) and at most 8.5 cm, and a mean diameter of atleast 2 cm and at most 3.5 cm.
 33. A pick tool as claimed in claim 32,in which the insertion shank is shrink-fitted within the bore.
 34. Apick tool as claimed in claim 32, in which the interference between theinsertion shank and the bore is at least 0.002 percent of the diameterof the insertion shank and at most 0.3 percent of the diameter of theinsertion shank.
 35. A pick tool as claimed in claim 33, in which theinterference between the insertion shank and the bore is at least 0.002percent of the diameter of the insertion shank and at most 0.3 percentof the diameter of the insertion shank.
 36. A pick tool as claimed inclaim 32, in which the support body comprises cemented carbide materialcomprising at most 10 weight percent metal binder material.
 37. A picktool as claimed in claim 33, in which the support body comprisescemented carbide material comprising at most 10 weight percent metalbinder material.
 38. A pick tool as claimed in claim 32, in which thesupport body comprises cemented carbide material comprising grains ofmetal carbide having a mean size of at most 8 microns.
 39. A pick toolas claimed in claim 33, in which the support body comprises cementedcarbide material comprising grains of metal carbide having a mean sizeof at most 8 microns.
 40. A pick tool as claimed in claim 36, in whichthe support body comprises cemented carbide material comprising grainsof metal carbide having a mean size of at most 8 microns.
 41. A picktool as claimed in claim 32, in which the ratio of the volume of thecemented carbide support body to the volume of the superhard tip is atleast 30 and at most 300, and the volume of the superhard tip is atleast 200 mm³ and at most 500 mm³.
 42. A pick tool as claimed in claim32, in which a surface area of the insertion shank abuts a correspondinginner side surface area of the bore, the surface area being at least 20cm².
 43. A pick tool as claimed in claim 32, in which a portion of theinsertion shank is only partly surrounded by the bore of the steelholder.
 44. A pick tool as claimed in claim 32, in which the steelholder is provided with a seat for supporting an end of the cementedcarbide support body, and the bore communicates with the outside of thesteel holder through a passage provided through or adjacent the seat.45. A pick tool as claimed claim 32, in which the superhard tipcomprises diamond material.
 46. A pick tool as claimed claim 33, inwhich the superhard tip comprises diamond material.
 47. A pick tool asclaimed claim 37, in which the superhard tip comprises diamond material.48. A pick tool as claimed claim 38, in which the superhard tipcomprises diamond material.
 49. A pick tool as claimed in claim 32, inwhich the superhard tip comprises a polycrystalline diamond (PCD)structure bonded to a cemented carbide substrate.
 50. A pick tool asclaimed in claim 33, in which the superhard tip comprises apolycrystalline diamond (PCD) structure bonded to a cemented carbidesubstrate.
 51. A pick tool as claimed in claim 32, in which thesuperhard tip comprises diamond grains dispersed in a cemented carbidematrix.
 52. A method of making a pick tool as claimed in claim 32, themethod including providing an insert and a steel holder for the insert,the insert comprising a superhard tip joined to a cemented carbidesupport body having an insertion shank; the steel holder comprising ashaft for connection to a tool carrier and the steel holder providedwith a bore for receiving the insertion shank; the insertion shankhaving a volume of at least 10 cm³; and shrink fitting the insertionshank into the bore of the steel holder; in which the cemented carbidesupport body has a volume of at least 15 cubic centimetres (cm³) andcomprises cemented carbide material having fracture toughness of atleast 8 megapascals times square root metre (MPa·m^(1/2)) and at most 17MPa·m^(1/2); and in which an inserted portion of the insertion shank issecured in the bore, the inserted portion having an axial length of atleast 4 centimetres (cm) and at most 8.5 cm, and a mean diameter of atleast 2 cm and at most 3.5 cm.
 53. A method of disassembling a pick toolas claimed in claim 32, the method including heating the steel holder toexpand the bore and withdrawing the insertion shank from the bore.